JP3935348B2 - Heat exchange tube and method for manufacturing the same - Google Patents

Abstract

A metallic heat exchanger tube, especially for vaporizing liquids comprising pure materials and mixtures on the outside of the tube, comprises integral ribs (3) on the outside of the pipe, which have a foot (13) that extends radially from the pipe wall (18). Grooves between the ribs have cut-outs in the base. The cut-outs are in the form of cut-back secondary grooves (7).

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a metal heat exchange tube according to the superordinate concept of claim 1, and more particularly to a metal heat exchange tube for evaporating a liquid composed of a pure substance or a mixture.
[0002]
[Prior art]
Evaporation takes place in many areas of refrigeration technology and air conditioning technology, as well as process technology and energy technology. In such a technique, a tube heat exchanger is often used. In the tube heat exchanger, a pure substance or a liquid mixture evaporates on the outer surface of the tube, and salt water or water is cooled on the inner surface of the tube. Is done. Such an apparatus is called a full liquid evaporator.
[0003]
By increasing the heat transfer on the outer and inner tube surfaces, the evaporator size can be significantly reduced. This reduces the manufacturing cost of this type of device. Furthermore, the required refrigerant charge is reduced. In the case of a safe refrigerant not containing chlorine, which is mainly used today, the refrigerant may occupy a cost that cannot be ignored in the overall equipment cost. Further, in the case of a toxic refrigerant or a flammable refrigerant, the risk factor can be reduced. High performance tubes used today are superior in performance by almost three factors compared to smooth tubes of the same diameter.
[0004]
The present invention relates to a structured tube that increases the heat transfer coefficient of the outer surface of the tube, but in this type of structured tube, the main component of the heat flow resistance often moves to the inner surface. Usually, the heat transfer coefficient of the inner surface must also be increased. Increasing heat transfer on the tube inner surface usually results in increased pressure drop on the tube side.
[0005]
Heat exchange tubes for tubular heat exchangers typically have at least one structured region, a smooth end member, and possibly a smooth intermediate member. The smooth end member or intermediate member defines a structured area. In order for the tube to be replaceable in the tubular heat exchanger, the outer diameter of the structured area should not be greater than the outer diameter of the smooth end member and intermediate member.
[0006]
In order to increase heat transfer during evaporation, the bubble boiling process is enhanced. It is known that bubble formation begins at nucleation sites. This nucleation site is most often a small gas or vapor containing part. Such nucleation sites can already be generated by roughening the surface. When the growing bubble reaches a certain size, the bubble dissociates from the surface. When the liquid flows into the nucleation site following the dissociation of the bubbles, in some cases, the gas-containing part or the vapor-containing part is excluded by the liquid. In this case, the nucleation site becomes inactive. This can be avoided by appropriately configuring the nucleation site. For this purpose, it is necessary that the opening of the nucleation site is smaller than the hollow space under the opening.
[0007]
According to the prior art, this type of structure is manufactured on the basis of a finned tube that is rolled together. The finned tube rolled integrally is a finned tube obtained by molding a fin from a wall material of a smooth tube. Various methods are known in this case, but the pipe line between the fins is closed to leave the communication part between the pipe line and the periphery in the form of a hole or a slit. Since the opening of the hole or slit is smaller than the width of the conduit, the conduit is a suitably shaped hollow space that favors the formation and stabilization of the bubble nucleation site. In particular, this kind of closed conduit is produced by bending or bending the fin (US 3.696.861, US 5.054.548), produced by tearing and compressing the fin. (DE 2.758.526, US 4.577.381), and those generated by forming notches in the fins and compressing them (US 4.660.630, EP 0.713.072, US 4.216.826) is there.
[0008]
High performance finned tubes for full-vapor evaporators available on the market have a fin density of 55 to 60 fins per inch on the fin outer surface (US5.669.441, US5.6977). 430, DE 19757526). This corresponds to a fin pitch of approximately 0.45 mm to 0.40 mm. Higher fin density or smaller fin pitch can improve the performance of this type of tube. This is because the density of bubble nucleation sites is increased. To make the fin pitch smaller, a uniform and fine tool is absolutely necessary. However, fine tools have a high risk of breakage and wear quickly. Recently used tools allow reliable production of up to 60 finned tubes per inch with fin densities up to. Furthermore, as the fin pitch is reduced, the production rate of the tube is reduced, resulting in increased manufacturing costs.
[0009]
It is known that by using the bottom of the groove between the fins, it is possible to produce a high-performance evaporation structure with a uniform fin density on the outer surface of the tube. EP 0.222.100 proposes using a notch disk to provide a recess at the bottom of the groove. The recess at the bottom of the groove has a V-shaped, trapezoidal or semicircular cross-section and forms an auxiliary bubble nucleation site. However, the performance gains that can be obtained with this type of structure, especially in the low heat flux region, are never sufficient for market demand. The recess also weakens the core wall of the tube and reduces the mechanical stability of the tube.
[0010]
[Problems to be solved by the invention]
It is an object of the present invention to provide a high performance heat exchange tube for evaporating liquid on the outer surface of a tube that has the same heat transfer and pressure drop on the tube side and is manufactured at the same manufacturing cost. It is also to avoid adversely affecting the mechanical stability of the tube.
[0011]
[Means for Solving the Problems]
According to the present invention, in the heat exchange pipe of the above type, in which the drawing-out portion is arranged in the region of the groove bottom of the primary groove extending in a threaded manner between the fins, the drawing-out portion is The problem is solved by forming the concave groove in the shape of a secondary groove.
[0012]
Recessed grooves (see Figure 1) are present
-When an unclosed region X is found in the cut plane,
-If this region X can be closed by the section AB, and-the section PQ including P and Q that are part of the edge of the region X is found, so that PQ is parallel to AB and the length of the PQ Is longer than the length of AB,
It is.
[0013]
Recessed secondary grooves provide clearly favorable conditions for the formation and stabilization of bubble nucleation sites compared to the simple recesses proposed in EP 0.222.100. The concave secondary groove is located near the primary groove bottom, which is particularly advantageous for the evaporation process. This is because at the bottom of the groove, the wall overheating is at its maximum, and therefore the bubble formation promoting temperature difference is at its maximum.
[0014]
Claims 2 to 15 relate to advantageous embodiments of the heat exchange tube according to the invention.
[0015]
According to the present invention, after forming the fin with a suitable auxiliary tool, the material is removed from the region of the fin side towards the groove bottom, resulting in a hollow space that is not completely closed, these The hollow space forms a secondary groove having a desired concave angle. The hollow space extends from the primary groove bottom toward the fin tip, and in this case the expansion of the hollow space is at most 45% or less of the fin height H, typically 20% or less of the fin height H. is there. The fin height H is measured from the deepest position of the groove bottom formed by the largest rolling disk to the fin tip of the completely formed finned tube.
[0016]
Furthermore, according to claims 16 to 22, various methods for producing the heat exchange tubes according to the invention are also the subject of the invention.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail.
[0018]
The integrally rolled finned tube 1 shown in FIGS. 2 to 7 has fins 3 that circulate in a threaded manner on the outer surface of the tube, and a primary groove 4 is formed between the fins 3. Yes. The material of the fin side surface 5 is moved appropriately, resulting in a hollow space 7 which is not completely closed in the region of the groove bottom 6, which is a concave secondary groove according to the invention. The material of the fin tip 8 is moved so that the fin intermediate space is closed except for the hole 26 to form the conduit 9.
[0019]
The production of the finned tube according to the invention is carried out by means of a rolling process (see US 1.865.575, US 3.327.512) using the apparatus illustrated in FIGS.
[0020]
The apparatus to be used consists of n = 3 or 4 tool holders 10, and a rolling tool 11 is incorporated in each of these tool holders 10. The tool holders 10 are arranged around the finned tube so as to be shifted by 360 ° / n. The tool holder 10 can be adjusted in the radial direction. The tool holder 10 is disposed in a stationary rolling head (not shown).
[0021]
The smooth tube 2 that runs into the apparatus in the direction of the arrow is rotated by a rolling tool 11 that is arranged and driven around it, and in this case, the axis of the rolling tool 11 extends obliquely with respect to the tube axis. The rolling tool 11 includes a plurality of rolling disks 12 arranged in parallel with each other in a known manner, and the diameter of the rolling disk 12 increases in the direction of the arrow. The rolling tool 11 arranged in the center forms fins 3 extending in a threaded manner from the tube wall of the smooth tube 2, in which case the tube wall is supported from below by a rolling mandrel 27 in the forming zone. The rolling mandrel 27 may be irregular. The interval measured in the direction along the tube axis line between the centers of two adjacent fins will be referred to as a fin pitch T. The rolling disk has an outer periphery that is shaped so that the molded fin 3 has a substantially trapezoidal cross section. The fin differs from the ideal trapezoidal shape only in the transition region 13 between the fin side surface 5 and the groove bottom 6. This transition region 13 is usually called a fin foot. The radius formed there is necessary to allow an unobstructed flow of the material during molding of the fin.
[0022]
After forming the substantially trapezoidal fin 3 with the rolling tool 11, the concave secondary groove 7 according to the present invention is generated in the region of the groove bottom 6 of the primary groove 4. In this case, three different embodiments can be applied.
[0023]
Embodiment 1
A cylindrical disk 14 is engaged after the last disk of the rolling tool 11 and its diameter is smaller than the diameter of the largest rolling disk (FIG. 2). The thickness D of the cylindrical disk 14 is somewhat larger than the width B of the primary groove 14 formed by the rolling disk 12. The width B of the primary groove 4 is measured at a location where the fin side surface 5 has shifted to the radial region of the fin foot portion 13. Typically, the thickness D of the cylindrical disk is 50% to 80% of the fin pitch T. The cylindrical disk 14 removes material from the fin side surface 5 toward the groove bottom 6. The rejected material is moved by appropriate selection of the tool geometry to form a material projection 15 above the groove bottom 6 and thus a hollow space 7 that is not completely closed directly on the groove bottom 6. (FIG. 3). The hollow space 7 extends in the circumferential direction with a substantially uniform cross section. The hollow space 7 is a concave secondary groove according to the present invention.
[0024]
Providing the side surface of the disk 14 with a completely concave profile or a partially concave profile along the circumference of the disk is expedient because it facilitates the discharge of the material of the fin side 5 There was found.
[0025]
Since the diameter of the cylindrical disk 14 is smaller than the diameter of the largest rolling disk of the rolling tool 11, the deepest portion of the primary groove bottom 6 is not processed by the cylindrical disk 14. Accordingly, the tube wall 18 is not weakened when the concave secondary groove 7 is formed.
[0026]
Embodiment 2
This embodiment is an extension of the first embodiment. In the second embodiment, there is a gear-shaped notch disk 16 after the cylindrical disk 14 and the diameter thereof is larger than the diameter of the cylindrical disk 14, but at most the rolling tool 11 has a diameter. It is the size of the diameter of the largest rolling disc. A hollow space formed by the cylindrical disk 14 and extending with a uniform cross section in the circumferential direction is divided by the notch disk 16 into dents 17 regularly arranged in the circumferential direction. As a result, a concave secondary groove 7 that circulates in the circumferential direction is generated, and its cross section changes at regular intervals (FIG. 5). The notch disk 16 may be linearly toothed or inclined and toothed.
[0027]
Since the diameter of the gear-shaped notch disk 16 is not larger than the diameter of the largest rolling disk of the rolling tool 11, the deepest portion of the primary groove bottom 6 is not deepened further by the gear-shaped notch disk 16. Therefore, the tube wall 18 is not weakened when forming the concave secondary groove 7 according to the second embodiment.
[0028]
Embodiment 3
A gear-shaped notch disk 19 is engaged after the last disk of the rolling tool 11, and the diameter of the notch disk 19 is at most the same as the diameter of the largest rolling disk (FIG. 6). The thickness D ′ of the notch disk 19 is somewhat larger than the width B of the primary groove 4 formed by the rolling disk 12. The width B of the primary groove 4 is measured at a location where the fin side surface 5 moves to the radial region of the fin foot 13. Typically, the thickness D ′ of this notch disk is 50% to 80% of the fin pitch T. The notch disk 19 may be linearly toothed or inclined and toothed. The notch disk 19 removes material from the area of the fin side surface 5 and the radius area of the fin foot 13 and leaves indentations 20 that are spaced apart from each other. The rejected material is preferably displaced into the unmachined area between the individual recesses 20, so that a dam 21 is stamped there so as to extend between the fins 3 in a direction transverse to the primary groove 4. Occurs. The next finishing rolling disk 22 having a constant diameter forms the upper region of the damming portion 21 in the pipe circumferential direction, and as a result, between the shaped upper region 23 of the damming portion 21 and the groove bottom 6, A small hollow space 7 is formed so as to be positioned between two adjacent damming portions 21 (FIG. 7). These hollow spaces 7 are secondary grooves having a concave angle according to the present invention. The diameter of the finishing rolling disk 22 needs to be selected smaller than the diameter of the base notch disk 19.
[0029]
Since the diameter of the gear-shaped notch disk 19 is not larger than the diameter of the largest rolling disk of the rolling tool 11, the deepest portion of the primary groove bottom 6 is not further deepened by the gear-shaped notch disk 19. Therefore, the tube wall 18 is not weakened when forming the concave secondary groove 7 according to the third embodiment.
[0030]
After the concave secondary groove 7 is formed in the groove bottom 8, a notch is formed in the fin tip 8 using a gear-shaped notch disk 24. This is illustrated in FIG. 2, FIG. 4 and FIG. Next, the tip of the fin in which the notch is formed is flattened by one or a plurality of flattening rollers 25. In this way, the fins 3 have a substantially T-shaped cross section, and the grooves 9 between the fins 3 are closed except for the holes 26 (see FIGS. 3, 5, and 7).
[0031]
The fin height H of the completed finned tube 1 is measured from the deepest part of the groove bottom 6 to the fin tip of the completely shaped finned tube.
[0032]
The concave secondary groove 7 formed in the groove bottom 6 of the primary groove 4 according to the present invention extends from the groove bottom 6 toward the tip of the fin, and in this case, the expansion is maximum and the fin height H is increased. Up to 45%, typically up to 20% of the fin height H.
[0033]
FIG. 8 is a photograph of the concave secondary groove 7 formed in the groove bottom 6 according to the present invention. The cross section is a direction perpendicular to the circumferential direction of the tube. This photograph is an example according to the first embodiment. It can be seen that the structure is asymmetric, due to unavoidable tolerances in tool dimensions and material dimensions. The protrusion 15 is made of a material moved from the fin side surface 5 toward the groove bottom 6.
[0034]
FIG. 9 compares the performance of two structured tubes when evaporating the freezing agent R-134a on the outer surface of the tube, and one of the two tubes has two concave corners at the groove bottom. The next groove is provided. The figure shows the relationship between the outer heat transfer coefficient and the heat flux. The saturation temperature in this case is 14.5 ° C. As can be seen, the concave secondary groove at the bottom of the groove achieves a performance advantage of 30% or more when the heat flux is small and nearly 20% when the heat flux is large.
[0035]
A structure having a concave secondary groove at the groove bottom is also proposed in EP 0.522.985. However, the structure in this case is on the inner surface of the tube. In order to ensure the mechanical stability of this type of tube, especially when expanding the tube, the secondary groove must be configured as flat as possible. This is achieved by the acute angle shape of the secondary groove, as described in EP 0.522.985. When the freezing agent on the side surface of the tube is evaporated, a pressure higher than that of the outer surface of the tube is usually dominant inside the tube. With internal pressure loading, the mechanical load on the tube wall increases due to the notch action of the sharp edge of the secondary groove. This must be compensated by the thicker wall. However, this safety margin increases the amount of material used and thus increases costs.
[0036]
【The invention's effect】
As proposed by the present invention, if the concave secondary groove 7 is formed in the region of the primary groove bottom 6 on the outer surface of the finned tube, the tube wall 8 is not weakened. This is because only the material in the region of the fin side surface 5 and possibly the material in the radial region 13 above the groove bottom 6 is used for forming the secondary groove 7.
[Brief description of the drawings]
FIG. 1 is a basic configuration diagram of a recessed groove.
FIG. 2 is a view schematically showing a method of manufacturing a heat exchange tube according to the present invention, which has a concave secondary groove having a substantially constant transverse cross-section and spirally wound around the outer surface of the tube.
FIG. 3 is a partial view of a heat exchange tube according to the present invention with a concave secondary groove that circulates in a threaded manner with a substantially constant cross-section.
FIG. 4 schematically shows a method of manufacturing a heat exchange tube according to the present invention, comprising a secondary groove having a concave angle that circulates in a threaded manner, and the cross section of the secondary groove changes at regular intervals. FIG.
FIG. 5 is a partial view of a heat exchange tube according to the present invention comprising a secondary groove having a concave angle that circulates in a threaded manner, and the cross section of the secondary groove changes at regular intervals.
FIG. 6 is a diagram schematically showing a method of manufacturing a heat exchange tube according to the present invention having a recessed secondary groove extending substantially transversely to the direction of the primary groove.
FIG. 7 is a partial view of a heat exchange tube according to the present invention with a recessed secondary groove extending substantially transversely to the direction of the primary groove.
FIG. 8 is a photograph of a concave secondary groove according to the present invention that is spirally wound with a substantially constant cross section at the groove bottom.
FIG. 9 is a graph illuminating the performance advantage of a recessed secondary groove provided at the groove bottom.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tube with fin 2 Smooth tube 3 Fin 4 Primary groove 5 Fin side surface 6 Groove bottom 7 Secondary groove 8 Fin tip 12 Rolling disk 13 Fin foot 14 Cylindrical disk 16 Notch disk 19 Notch disk 20 Recess 22 Finish rolling disk 24 notch disk 25 flattening roller 27 rolling mandrel

Claims (15)

An integral fin (3) molded on the outer surface of the tube, with its foot (13) projecting from the tube wall (18) in a substantially radial direction, said fin having a substantially T-shaped cross-section; 3) a metal heat exchange tube provided with a withdrawal portion in the region of the groove bottom (6) of the primary groove (4) extending between 3), in particular for evaporating a liquid consisting of a pure substance or a mixture In metal heat exchange tubes,
The withdrawal part is formed in the shape of a secondary groove (7) having a substantially constant transverse section with a concave angle, and the fin (3) and the primary groove (4) extend in a threaded shape. A metal heat exchange tube. 2. A metal heat exchange tube according to claim 1, characterized in that the concave secondary groove (7) extends in the direction of the primary groove (4) with a substantially constant cross section. 2. The metal heat exchange tube according to claim 1, wherein the cross section of the concave secondary groove extending in the direction of the primary groove changes at regular intervals. The maximum width of the concave secondary groove (7) is 45, which is the height of the fin (H). % The metal heat exchange tube according to any one or more of claims 1 to 3, wherein: The maximum expansion of the concave secondary groove (7) is 20 of the fin height (H). % The metal heat exchange tube according to claim 4, wherein: The metal heat exchange tube according to any one or more of claims 1 to 5, wherein the fins (3) have a uniform height (H). The metal heat exchange tube according to any one or more of claims 1 to 5, wherein a notch is formed in the fin tip (8). 8. The metal heat exchange tube according to claim 1, wherein the metal heat exchange tube has a smooth end portion and / or a smooth intermediate region. 9. The metal heat exchange tube according to claim 1, wherein the metal heat exchange tube is formed as a seamless tube. 9. The metal heat exchange tube according to claim 1, wherein the metal heat exchange tube is formed as a vertical seam welded tube. In the manufacturing method of the heat exchange pipe | tube of Claim 1,
a) Obtaining fin material by removing material from the tube wall to the outside by a rolling process, rotating the resulting finned tube (1) by rolling force and / or advancing according to the resulting fin Rolling the fin (3) extending in a threaded manner on the outer surface of the smooth tube (2), and forming the fin (3) from the non-formed smooth tube (2) while increasing the height. When,
b) supporting the smooth tube (2) by a rolling mandrel (27) therein;
c) after molding the fin (3), the material is moved by radial pressure from the fin side (5) towards the groove bottom (6) and / or from the fin foot transition region (13) ( 6) moving to the direction of forming a concave secondary groove (7);
d) flattening the fin tip (8) with other radial pressures using at least one flattening roller (25) to produce a substantially T-shaped cross section;
The manufacturing method described above. In the manufacturing method of Claim 11 for manufacturing the heat exchange pipe | tube of Claim 2,
  Generating a radial pressure in step c) using a cylindrical disc (14);
Its diameter is smaller than the diameter of the largest rolling disc (12) and its thickness (D) is at least 50 of the fin pitch (T). % Up to 80 % The manufacturing method characterized by the above-mentioned. In the manufacturing method of Claim 12 for manufacturing the heat exchange pipe | tube of Claim 3,
  Subsequent to step c), step d) is carried out. The groove bottom (6) is partially shaped by other radial pressures using the disc disk (16) to produce recesses (17) that are regularly spaced from each other in the circumferential direction, A manufacturing method, characterized in that the diameter of the disk (16) is larger than the diameter of the cylindrical disk (14), but is at most as large as the diameter of the largest rolling disk (12). Notch discs (16 , The manufacturing method according to claim 13, wherein 19) is used. In the manufacturing method as described in any one of Claim 12-14 for manufacturing the heat exchange pipe | tube of Claim 7.
  In another step e), a notch is formed by radial pressure using a gear-shaped notch disk (24) at the fin tip (8).

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